The present invention relates generally to the field of physiological monitoring, particularly to the detection and monitoring of weak physiological signals in the presence of stronger signals of either physiological or non-physiological origin. Specifically, the invention relates to the separation of signals by resolving multiple equations describing data derived from multiple sensors.
In the field of physiological monitoring it is often desirable to measure a particular signal which may be obscured or confounded by additional, stronger, signals. The stronger signals may be dissimilar from the signal of interest, such as the signal attributable to equipment-induced vibration when measuring heart motion. In some cases, though, the signal may be similar to the signal of interest but of a much greater scale, such as maternal heart motion compared to fetal heart motion. In either case, it may be desirable to detect and monitor the weaker signal.
For example, it may be desirable to determine the fetal heart rate or the waveform associated with fetal heart beat to check for the presence of abnormalities or defects within the developing fetus. However, the fetal heart motion is typically obscured by the mother's respiration and heart movements. The additional movements affect the acquisition and quality of the desired fetal heartbeat data. Though accelerometers and other motion-sensitive detectors can collect data containing information on fetal heart motion, the information will be confounded, if not completely lost, in the presence of stronger, maternal physiological noise.
In such cases, increasing or adjusting the sensitivity of the detector is not a viable solution because the relative strength of the signal is the source of the problem, not the sensitivity of the detector. In the fetal heart monitoring example, the maternal heart motion and maternal respiration will always exceed the fetal heart motion in magnitude. Typically, maternal heart motion will be substantially greater than fetal heart motion. Therefore, a system for monitoring fetal heart motion must be able to separate the fetal heart motion from the stronger components of detected motion such as maternal heart motion, maternal respiration, and non-periodic motion components attributable to the movement of the fetus or mother.
Maternal respiration may be separated from the other responses due to its lower frequency content, which is separable by highpass filtering. However, due to their similarity, maternal and fetal heart motion components typically cannot be separated from one another based on frequency information alone. Therefore, point measurements from a single sensor are inadequate for separating these heart motion components.
Other situations exist where it may be desirable to detect and monitor a weak physiological signal in the presence of a much stronger non-physiological signal. For instance, medical equipment or mechanical devices may produce significant vibration which can obscure a weaker, physiological signal, such as heart motion. In such cases the heart motion and non-physiological vibration may be confounded, making detection and monitoring of the physiological signal impractical using point measurements from a single sensor.
There is a need, therefore, for an improved technique for detecting and monitoring weak physiological signals, such as fetal heart motion, in the presence of stronger physiological and non-physiological signals. To address the drawbacks in heretofore known systems, there is a particular need for a technique which can be employed in a straightforward manner to allow a relatively weak set of signals to be discerned from relatively stronger signals associated with other physiological signals or with non-physiological signals.